Back to the old topic of those spikes that at least some of us see from time to time.
I have a new neighboring station. just a few miles away, with a small “mountain” between us.
I saw a large spike this morning:
This is a Shake-Boom. The spike only occurs on the EHZ channel, no trace of it on HDF (infrasound).
So I thought I would take a look at my neighbor. He has a 3D.
His EHZ channel:
Hmmm… he sees a big spike too, but a lot later than I did. It gets more interesting looking at the other channels:
Not a sign of the spike on those channels.
So it is picked up by the Z channel, but not by N or E channels.
I can only conclude that is is a vertical ground movement, or, just maybe, a very polarized (strong) EMF signal.
Very strong signals, but neither one picked up by the other station, so very local, but strong.
This leads me back to an old theory of mine which is now looking likely (at least to me) again: Both devices are (as far as I am aware) sitting on large concrete floor slabs of out buildings. I think what we are seeing is expansion/contraction due to temperature changes causing stress movements within the concrete (or maybe the buildings themselves?).
Interesting hypothesis! Mine is in the corner of a 36’ishX80ish concrete floored workshop.
Mine is approx 30x60 pole barn - concrete floor. Not quite in the corner, but close to the wall.
I’ve seen this before on my home made seismometer that was made from accelerometers. It was a 3D accelerometer. After throwing out bad sensor reads, I would get these types of spikes. They would only be for a single sample, and they would only affect one axis at a time. There would be no rebound that you would see from typical motion where you speed up and slow down.
This type of stuff is what you see from ionizing radiation. Most computers harden themselves from this error inducing scenario by using checksums and other fault recovery techniques. What’s typically happening is that a bit is flipped in the sensor read, which can significantly alter the value read from the sensor. The flipped bit is typically overridden by the next sample read. Normally this is a rare occurrence.
If you listen to the Radiolab podcast titled Bit Flip, you’ll hear about other scenarios where computers fail when encountering ionizing radiation.
Ionizing radiation is everywhere. The level of radiation is higher in some places and lower in others. You can shield your sensor to reduce the incidence of it, but it can’t be eliminated. It’s a natural phenomenon that is unrelated to earthquakes.
I did consider cosmic ray hits. It’s a possibility. the reason I disregarded it was because it is not a single sample that shows an extraordinarily high/low value.
Looking at the trace, we see typically something like this:
The recorded data for the period of the spike:
As you can see the dip (in this case) is not instantaneous, and the recovery even less so.
As far as I know, the counts values are pretty much raw data from the accelerometer. I don’t think there is any sort of filter between which might result in ringing effects. Although … the spikes always have pretty much this form: rapid increase/decrease, with a slower recovery and small overshoot.
Maybe someone with a bit of knowledge of the actual architecture of the digitization board might care to comment on whether there is any sort of filter that might ring (although if so, it is fairly well damped) with sudden step values in readings?
Added: The temperatures have been fairly constant (low to high 50s °F) for the past week, and looking for examples of spikes, I didn’t find any really good examples, just the one above, which is pretty small compared to those seen during the summer when there were much wider temperature swings.
I see interference when operating radio transmitters around my SB (I am a Ham Radio operator). I have suspected that aircraft radio above or near my house could be enough to cause similar anomalies, but have yet to well-correlate this.
I see this too - especially when I run about 1Kw
Not really surprised. I did think about building a faraday screen, with just three holes in the bottom for the R-Shake support “pins” (and of course for the power and Ethernet cables - with ferrite beads inside and out. But at the moment, I don’t do enough operating to make that a priority.
I did look at the possibility of radio-altimeter pulses from aircraft approaching/leaving PDX. But there was just no correlation between overhead aircraft and the spikes - besides, those radio pulses are not that powerful.
A few watts on 160M or 80M is enough for mine to produce spikes. My Shake is in the near field of several antennas.
I’ve tried toroids, and whatever Faraday Cage I have tried to make cannot be made RF-dense enough to stop everything from 160M-70cM without also becoming a resonant drum that causes high incident noise on the shake. I just live with the knowledge that I might miss some things when operating.
My shake and boom did manage to pick up both the seismic event and the sound event from the Tongan eruption this year, so it’s doing well.